magnetic field – Sciblogshttps://sciblogs.co.nz
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1 https://wordpress.org/?v=5.2.3https://sciblogs.co.nz/app/uploads/2019/04/cropped-SciBlogsFBProfile-32x32.jpgmagnetic field – Sciblogshttps://sciblogs.co.nz
3232The problem with undergraduate textbooks…https://sciblogs.co.nz/physics-stop/2018/08/07/the-problem-with-undergraduate-textbooks/
https://sciblogs.co.nz/physics-stop/2018/08/07/the-problem-with-undergraduate-textbooks/#respondTue, 07 Aug 2018 00:08:51 +0000https://sciblogs.co.nz/?p=257732In the last few weeks I’ve been talking with a colleague about magnetizable materials – what they do and how they are categorized.

I’m talking about things such as iron – which, when you put them in a magnetic field, will magnetize. That makes the field bigger than you started with. Some materials will stay magnetized when you take them out of the external magnetic field (these are called ‘hard’ materials – nothing to do with their physical toughness), and some won’t (or will only weakly – these are called ‘soft’ materials).

One of the properties that characterizes a magnetic material is the ‘relative permeability’ – often given the Greek letter ‘mu’ with a suffix ‘r’ for ‘relative’. It tells us (sort of) how much a magnetic field will boost by, compared to air, if you use a magnetic material instead of air. Now, reading the undergraduate textbooks, (certainly the general ones focused on first-year) one would be forgiven for thinking that mu_r was just a scale factor you could multiply by to get the field in an object. For example, if you knew that a coil of wire with a certain current gave a magnetic field of 0.1 tesla, and you had a lump of magnetic material of relative permeability 100, then if you put that lump in the coil the field by the lump would be 100 times 0.1 = 10 tesla.

No. Two problems (at least). First, the relative permeability is never a constant. As the field strength increases, relative permeability will plummet. No way are you going to get to 10 tesla. But there’s a more fundamental problem. First-year textbooks often present unrealistic hypothetical examples. The favourite is the infinite solenoid – a coil of wire of infinite length. There’s a very good reason why this is presented – because you can do the maths! Now, in this case, if you insert an infinitely long magnetic rod inside the coil to totally fill the space, the magnetic field will indeed boost mu_r times – so what was 1 tesla will become 100 tesla in our example. But this is a hopelessly stereotyped example. One never has a core of infinite length. In practice, fields are going to be much less.

In fact, one other situation (go to third-year undergraduate texts or above) which CAN be solved exactly is what happens when you put a magnetizable sphere inside a magnetic field. The result is surprising – when mu_r is large, the boost in the field will come to 3. No more. Our 0.1 tesla field boosts to 0.3 tesla. That’s because the sample doesn’t cover the entirety of space.

My point here is that textbooks can, in their effort to create solvable mathematical problems in physics, bypass what is physically reasonable and create misconceptions.

One could say the mistake actually is to think that it is the mathematics which is important. Here at Waikato, we’ve just run a first-year paper ‘Physics in Context’, that has been designed to be accessible to the least mathematically-able science student. We’ve followed the paper closely, with some research that will be presented at an upcoming conference on the Australasian Association for Engineering Education, and I can confidently say that our students have learned the physics. But they didn’t need the much maths to do so.

]]>https://sciblogs.co.nz/physics-stop/2018/08/07/the-problem-with-undergraduate-textbooks/feed/0Science Tank | The Mighty Aurorahttps://sciblogs.co.nz/guestwork/2017/12/14/science-tank-mighty-aurora/
https://sciblogs.co.nz/guestwork/2017/12/14/science-tank-mighty-aurora/#respondWed, 13 Dec 2017 22:30:51 +0000https://sciblogs.co.nz/?p=249338Living far from the equator can be a bit of a bummer – we miss out on that awesome high concentration of sunshine and long sunny days. Instead we crawl sadly into our damp Dunedin caves at 4pm when we lose the sun in winter. We brave the cold Antarctic winds and surf in what feels like a frozen margarita all year around, never daring to risk a shorty wetsuit, even in summer. The upside to all of this? We are one of the very few places on Earth that gets treated to the aurora!

Aurora Australis, also known as the Southern Lights, translates to “dawn of the south” (while our neighbours to the north call it Aurora Borealis, the “dawn of the north”) and it is the most spectacular display of atmospheric chemistry mankind can bear witness to.

Earth’s atmosphere is a smorgasbord of gases – mainly nitrogen and oxygen with a casual clustering of helium, hydrogen and some other random stuff.

Surrounding our planet is a geomagnetic field, which protects us and our ozone layer from the cosmic rays, and their dastardly mates the charged particles of solar winds. This magnetic field is pretty much due to our molten iron innards, which is essentially Earth’s ‘magnet’ – the magnetic field propagates from this core out into space and back in through the poles. The magnetic field is full of electrons and positive ions, which means that it is always ready to party. And party it does!

The Sun also has an atmosphere and a magnetic field, mainly because it’s a smug story-topper, but also probably because it’s a huge guy in space. The sun exists in a plasma state, and its atmosphere is composed of hydrogen, containing ions (charged particles) and electrons, which exist in such a high energy state that they just shoot off into space, escaping the Sun’s gravity. This is what we refer to as “solar wind”.

The Solar Wind

The solar wind is always acting a damn fool and harassing Earth’s magnetic field, causing the magnetic field’s shape to change, resulting in a compressed field around the Earth, known as the magnetosphere. The magnetosphere is full of built-up energy from the solar winds, and this is the power that drives the auroras.

When pressure from the solar winds builds up in the magnetosphere, an electric voltage is created, which runs from the magnetosphere to the poles, reaching up to 10,000 volts. Exacerbated by solar storms, this accelerates electrons to the poles and forces them down into the ionosphere (the upper layer of our atmosphere).

Remember how our atmosphere is full of gases?

Now that these speeding electrons are all up in our atmosphere, they begin smashing into those gases, feeding the gas atoms energy, which results in them emitting photons (light) and more electrons. You could say that the gases in the ionosphere act as conductors for electric currents in and out of the poles.

This view of the Aurora Australis, or Southern Lights, which was photographed by an astronaut aboard Space Shuttle Discovery (STS-39) in 1991, shows a spiked band of red and green aurora above the Earth’s Limb. Calculated to be at altitudes ranging from 80 – 120 km (approx. 50-80 miles), the auroral light shown is due to the “excitation” of atomic oxygen in the upper atmosphere by charged particles (electrons) streaming down from the magnetosphere above. Credit: NASA

The light emitted as photons from the smashing of electrons and atoms are what we see as the auroras, and the colours are indicative of where in the atmosphere the electrons are interacting with the gas, and which gas is involved. Oxygen gives off a greenish yellow colour or a red (depending on how high up the interaction is), while nitrogen gives off a blue tint. These colours all mix together, which is how those vivid purples and pinks appear.

If you’re keen to cast your juicy orbs on an aurora, the best places in Dunedin to check it out are Hooper’s Inlet and Blackhead Quarry. Dunedin Aurora Hunters is a group on Facebook that shares information and advises when auroras will be visible – so take a blanket, turn off all light sources and delight in the cosmic beauty afforded to us – because we are truly lucky to be able to see it.

Chelle Fitzgerald is a geology student and science writer living in Dunedin, New Zealand. She loves Jurassic Park and red wine.

This article was originally published by Critic te Arohi, the University of Otago’s student magazine. Artwork is by the wonderful Ceridwyn Giddens – check out her work here!

]]>https://sciblogs.co.nz/guestwork/2017/12/14/science-tank-mighty-aurora/feed/0Rare glimpse of a black hole’s magnetic field could help us to understand how it feedshttps://sciblogs.co.nz/guestwork/2017/12/12/rare-glimpse-black-holes-magnetic-field-help-us-understand-feeds/
https://sciblogs.co.nz/guestwork/2017/12/12/rare-glimpse-black-holes-magnetic-field-help-us-understand-feeds/#respondTue, 12 Dec 2017 00:30:38 +0000https://sciblogs.co.nz/?p=249266Carole Mundell, University of Bath

Encountering a black hole would be a frightening prospect for our planet. We know that these cosmic monsters ferociously devour any object that strays too close to their “event horizon” – the last chance of escape. But even though black holes drive some of the most energetic phenomena in the universe, the physics of their behaviour, including how they feed, remains hotly debated.

In particular, the conditions close to the black hole and the role of its magnetic fields are thought to be key, but are notoriously difficult to probe in distant cosmic systems. Now an international team of astronomers have for the first time measured the precise magnetic field properties close to a black hole in our own Milky Way galaxy.

The results of study, published in Science, could help us better understand the mysterious process by which black holes swallow matter and grow.

Predicted mathematically from Einstein’s theory of general relativity, we now think that black holes come in a range of sizes. Supermassive black holes – with a million to a billion times the mass of our sun and about the size of our solar system in extent – are thought to lie at the heart of all massive galaxies and are likely to play a decisive role in the formation and evolution of galaxies.

Artist’s impression of the surroundings of the supermassive black hole.ESO/M. Kornmesser, CC BY-SA

At the other extreme, there are black holes just a little more massive than our sun but contained in a region only a few kilometres across. They form in the cataclysmic death throes of massive stars or the merger of dense stellar remnants such as neutron stars or a neutron star colliding with another stellar black hole. When they merge, they produce gravitational waves.

Studies of gamma ray bursts (bursts of light with very high energy) have previously suggested that large-scale magnetic fields could form close to black holes and cause jets of charged gas to escape from them. A similar mechanism is expected for supermassive black hole systems, which launch jets that spread over distances of millions of light years and are visible to networks of radio telescopes such as the Very Large Array. However, even the nearest supermassive black hole is nearly 30,000 light years away from us, so it is technically challenging to probe their magnetic fields.

Cosmic burp

Cygnus.Till Credner/wikimedia

The new study looks at a black hole that lies only 8,000 light years from Earth, part of a “binary system”, dubbed V404 Cygni. This consists of a black hole with the mass of ten suns and a star similar to our own sun (but slightly cooler), which orbit each other every 6.5 days. In such systems, material from the star can fall towards the companion black hole to be gradually swallowed by it.

On its journey, the matter heats up, shines brightly and – in the presence of magnetic fields – some of it may be ejected back into space in the form of a focused beam of charged gas (plasma) or jets at bulk speeds close to that of light. Exactly how the magnetic fields cause this effect is still unknown. Luckily, the flares tend to be long-lived and their brightness can be monitored from Earth.

On June 15, 2015, V404 Cygni produced such an outburst – analogous to flares seen from the sun – that lasted for two weeks. The team, which immediately pointed a number of different telescopes at it, then noticed that the brightness of the system decreased suddenly and unexpectedly around June 25 across light frequencies ranging from X-rays to infrared.

They realised that this precipitous drop in brightness signalled that the system was cooling. By comparing this drop in brightness with models that predict how electrons produce light and lose energy – cool – when they spiral around magnetic field lines, the team were able to make a very precise estimate of the strength of the magnetic field. At 461 Gauss (a measurement of magnetism), this is much weaker than expected – only ten times stronger than a typical fridge magnet.

By studying how the properties of the light depended on frequency and time, they showed that the region from which the light was emitted was not expanding, as would be expected if the matter in this region formed part of a jet outflow. Instead, the research shows that there is a hot halo of charged particles held in place by a magnetic field around the black hole. The long-term fate of this halo gas is unknown, but it could be considered one of the last staging posts for fuel to reach the black hole and, if cooled further, may ultimately feed the black hole itself.

This work is important as it lays the foundations for future studies of this intriguing system to discover how black holes feed and how, if overfed, they may “burp” by launching focused beams or jets. Fortunately, V404 Cygni is sufficiently close to be an ideal laboratory for future studies of black hole feeding and cosmic indigestion, but far enough from Earth not to be a threat to us.

]]>https://sciblogs.co.nz/guestwork/2017/12/12/rare-glimpse-black-holes-magnetic-field-help-us-understand-feeds/feed/0Defecating dogs do it with directionhttps://sciblogs.co.nz/ice-doctor/2014/04/15/defecating-dogs-do-it-with-direction/
https://sciblogs.co.nz/ice-doctor/2014/04/15/defecating-dogs-do-it-with-direction/#respondTue, 15 Apr 2014 03:57:03 +0000https://sciblogs.co.nz/icedoctor/?p=88All that fussing around before they defecate may bemuse dog owners but it seems it’s about aligning N-S. Source: Wikimedia Commons, uploaded by Zoidy.

And why this research is unlikely to get funded in New Zealand

Last week I got to briefly talk science on George FM Breakfast. The invitation came care of my friend Clarke Gayford, the new George FM Breakfast co-host. I taught Clarke to ice fish in Antarctica (you can see our full escapades here) and perhaps as payback for making him occasionally take his gloves off in the great icy outdoors, he sent me this link to discuss what I thought about a particular item in the link: #5 Dogs use an internal compass when they poop.

Despite the seemingly unpleasant topic, the actual research article by Hart et al from the Czech Republic made for a very interesting, thought provoking read (popular press articles above and here). We’re very used to senses such as hearing, sight and taste but one that’s not very familiar to us is magnetoreception, where an organism can detect a magnetic field. This ability to sense magnetic fields is known as magnetosensitivity.

Several diverse animal species are known to align their body axis to magnetic fields (e.g. foxes, cattle, deer) and now we can add our canine friends to the list. In a two year study of 70 different dogs covering 37 breeds, an impressive total of 1893 defecation and 5582 urination events were recorded and then the data compared with magnetic field state at the time of excretion.

How did the researchers come up with such a seemingly left-field project? Magnetoreceptive behaviours happen across mammalian species in diverse contexts. Birds, bees, bats and bacteria as well as turtles, sharks and some other fish also snap to magnetic fields. For most species, the primary theory is that such alignment is used for navigation. Begall, one of the researchers in the dog study had previously found that grazing and resting cattle tend to align to magnetic field lines- you might remember this when it came out. This occurred when other factors (wind direction, sun position, curiosity) were negligible (unified herding behaviour possibly). We’ve probably all observed this too in clement weather, driving along past paddocks of cows wondering why they were all facing the same way.

The idea of magnetoreception is not viewed however, without skepticism. An attempt to replicate the cattle study by another group failed to find the same result- replication issues are becoming a major scientific issue, especially in the biomedical field. Begall and colleagues however, went on to use Google Earth aerial data to demonstrate the same finding as their original paper, suggesting their first results were indeed valid. They then looked at foxes and found they also seem to use magnetoreception when hunting (lining themselves up N-E for mousing jumps), and so looking at dogs became their next logical step (owing to homing ability and relationship to foxes).

They state that “dogs are still readily used as experimental animals”- somewhat of a difference between Eastern Europe and here, perhaps? Initially they looked for spontaneous alignment during a range of behaviours (resting, feeding, excreting) before, for reasons relating to number of independent data points, they settled on the least pleasant of all- excretion, including territory marking.

In a sensible move, 37 dog owners/reporters were recruited, meaning the researchers didn’t need to observe dog toiletries themselves. Dogs had to be unleashed and in unconstrained open field situations and away from high voltage power lines etc with defecation or urination measured with a handheld compass. It was only when the researchers looked at all their data and at the geomagnetic conditions at the time of each event that the researchers started to detect a significant pattern.

Magnetic declination is where there is a difference (or angle) between geographic (true) north (Ng) and magnetic north (Nm). It can be positive or negative . Source: Wikimedia Commons, uploaded by odder.

What was the pattern they found? During defecation both male and female dogs tend to align N-S. Whilst females stick to N-S during urination, males instead align N-W – this difference might be due to the classic leg-lift scenario in male dogs. However, doggy alignment for either #1’s or #2’s was only observed when the magnetic field was calm (it can vary greatly during the day and is typically only calm 20% of each day). When the magnetic field was unstable, any alignment of the dogs was abolished to the point where only 30% of excretion events saw conditions stable enough for alignment.

The best predictor for a shift in behaviour from aligning to no alignment was the degree of declination (deviation of magnetic north from true (geographic) north- which varies with place and time). Although the intensity of the magnetic field has been suggested to disturb alignment in birds and bees and other animals, this is the first time that declination itself has been examined.

I’m not sure though what was going on with one of the dogs in the study- a single male borzoi (Russian wolfhound) contributed 44% of the 5582 urination events, which in two years means 2456 pees, or 3.4 pees a day.

He should probably receive a dog treat for that effort or at least a kidney/bladder exam.

One participant in the study a borzoi contributed 44% of the 5582 urination events recorded over two years. Image source: Wikimedia Commons, Plepe2000

So what does all this lining up N-S or N-E mean for dogs when excreting (and their owners)? This is the bit that is a bit tricky- the authors simply don’t really know. Is it conscious (sensorially perceived) or do they just feel better doing it this way?

There are a few issues with the study, however. This study was a form of citizen science whereby recorders were the dog owners- it’s possible there were biases in data collection, adherence to the constraints (away from power lines, unleashed etc) that are unknown to the researchers, or that compass measurements weren’t always recorded accurately. One of the major issues from the results is that normal geomagnetic conditions only occurred during 30% of the excretion events recorded. That means that 70% of the time (majority) dogs were not excreting in alignment with magnetic fields.

One idea for why dogs do this alignment is that it is a bit like reading (and potentially creating) a road map and hence tied up with navigation. If the geomagnetic field is calm then the map is effectively in focus for the dog and they can respond to it by aligning. If the geomagnetic field is not calm, then the map is not in focus (in other words they can’t calibrate their landmarks, or visual map with the magnetic compass) and no alignment is possible. This may involve either over-riding or shutting down the actual magnetoreception mechanism. What exactly the mechanism is within cells remains to be seen.

Dog habits may frustrate owners but it appears there is a purpose- we just don’t know what the alignment for excretion means yet. Image source: Wikimedia Commons, uploaded by I see modern Britain.

This is where it gets tricky though from my perspective. Part of the activity of alignment while excreting could be to produce a ‘trail’ for them-self or even for others in a pack to follow. This is a more useful purpose perhaps, rather than just at the point they excrete conducting a check or calibration of the map. How then would they (or another dog in the pack following them, speaking of their evolutionary roots) differentiate when returning on that trail between a urination or defecation event that was done in alignment versus one that wasn’t and especially if when coming past the same point again the magnetic field was also unstable?

Also, the study is only observational in nature, albeit with correlations, and so there is a lot more need for mechanistic studies that actually look at what is happening inside the dog and inside cells to allow the proposed magnetoreception to occur. As such, it’s a starting point for further studies.

Just why dogs use the magnetic field to align themselves while defecating is still a mystery that only they know. Image source: Wikimedia Commons, uploaded by Brandon Weeks.

Why this research wouldn’t happen in New Zealand

The researchers involved were from the Czech Republic and Germany and the research was supported by a grant from the Czech Republic. This type of research would be classified as ‘blue skies’ research.

In New Zealand there has been a sustained and significant shift towards applied research for many years and we now have comparatively less blue skies research available, even if sum total of blue skies funds have increased over time. The major blue skies fund is the Marsden Fund, but it’s hard to envisage that the type of research presented in the article would be Marsden material.

There are smaller blue skies funds but again I can’t really imagine this research fitting nicely into many of those funding programmes either. It certainly doesn’t fit the mould of the new National Science Challenges- big, multidisciplinary projects tackling ‘the big issues’ facing New Zealanders. Even dog owners would probably agree it isn’t one of the big issues.

Thus, it’s unlikely that this kind of research would be funded within New Zealand. There are reasons though why perhaps research of this kind (not necessarily this work) should receive attention. Recently, there was an enlightening interview with the Nobel Prize winner Sydney Brenner on how academia and publishing are destroying scientific innovation.

In that interview, he discusses why the current research environment makes the kinds of breakthroughs he and his molecular biological colleagues made unlikely or near impossible today.

He said: “The supporters now, the bureaucrats of science, do not wish to take any risks. So in order to get it supported, they want to know from the start that it will work. This means you have to have preliminary information, which means that you are bound to follow the straight and narrow. There’s no exploration any more except in a very few places.”

Dog defecation studies might seem a strange pursuit. It’s just possible though that such studies have the potential to unlock something far more magical than doggy doo.

And true. Not the ones with which we’re all familiar, of course (and by these I am referring to the Giza structures).

[Interesting sidenote: bacteria are capable of building structures with sand, which they turn into sandstone, and there’s a fascinating TED talk which looks at how this ability could be used to build human habitats in the desert.]

I’m not going to try rephrase the article which IEEE Spectrum has written. That wouldn’t be fair. Nope, mainly I wanted to draw everyone’s attention to this remarkable development. You can watch the embedded video, below, to see how it happens.

But how do the scientists actually do this? Well, these types of bacteria contain magnetosomes: little organelles which are sensitive to magnetic fields and act as a sort of compass. To quote the IEEE article:

In the presence of a magnetic field, the magnetosomes induce a torque on the bacteria, making them swim according to the direction of the field. Place a magnetic field pointing right and the bacteria will move right. Switch the field to point left and the bacteria will follow suit.

Yes, the effect of each bacterium is tiny, but one of the great things about bacteria is their propensity to hang out in really big crowds. At which point all those tiny little forces add up to one rather less tiny force.

And what actual use could something like this have? Building nanoscale architectural monuments is fun, but hardly useful, after all. Well, having thought it out, the scientists realised that rather than trying to build tiny robots which mimic the behaviour of bacteria, and use said robots for functions such as drug delivery, organ repair and disease detection, it might be easier to use the tiny little robots nature has been so kind as to design already.

Clever stuff, this…

The paper detailing the advance can be found here, and is entitled “A Robotic Micro-Assembly Process Inspired By the Construction of the Ancient Pyramids and Relying on Several Thousands of Flagellated Bacteria Acting as Workers”. The structures involved may be tiny, but the titles apparently aren’t…